This invention relates to an apparatus for detecting a liquid level in a fuel tank of an automobile.
FIG. 12 shows such a kind of a related apparatus for detecting a liquid level. As shown in FIG. 12, the apparatus 100 includes a resistance plate 101, and a sliding arm 102 rotating on this resistance plate 101 in conjunction with rotation of a floating arm (not shown). A first sliding part 103, which is placed in a region that is apart from the center of rotation of the sliding arm 102, and a second sliding part 104, which is placed in a region that is close to the center of rotation thereof, are provided on a base 101a of the resistance plate 101. In the first sliding part 103, a plurality of first conductive segments 105 are arranged at certain intervals nearly in a sliding direction of the sliding arm 102, and any adjacent two of the first conductive segments 105 are connected to each other through a resistive element 106. In the second sliding part 104, a plurality of second conductive segments 107 are arranged at certain intervals nearly in the sliding direction of the sliding arm 102, and any adjacent two of the second conductive segments 107 are electrically conducted to each other by a conductive member that is the same as the second conductive segment 107. One end portion of each of the first sliding part 103 and the second sliding part 104 is set to be an E-point (that is, an empty point) portion 108. The other end portion of each of the first sliding part 103 and the second sliding part 104 is set to be an F-point (that is, a full point) portion 109. A connection land part 110 is electrically connected to each of the F-point portions 109. Lead wires (not shown) are connected to both the connection land parts 110, respectively. Detection outputs are obtained from both the connection land parts 110 through the lead wires.
The sliding arm 102 is constituted by a conductive member, and has a first contact part 120, which slides on the first sliding part 103, and a second contact part 121, which slides on the second sliding part 104. The first sliding part 103 and the second sliding part 104 are electrically connected to each other through this sliding arm 102.
In the case of the apparatus of the above configuration, when the sliding arm 102 rotates according to a liquid level, the first contact part 120 and the second contact part 121 slide on the first sliding part 103 and the second sliding part 104, respectively. The first contact part 120 comes in contact with a certain one of the conductive segments 105 of the first sliding part 103, while the second contact part 121 comes in contact with the second sliding part 104. Further, the main resistance of an electric circuit composed of the first sliding part 103, the sliding arm 102, and the second sliding part 104 is the resistance of the resistive element 106 disposed between the F-point portion 109 of the first sliding part 103 and the first conductive segment 108 with which the first contact part 120 comes in contact. Thus, a quantity of electricity corresponding to the sliding position of the sliding arm 102, that is, to the liquid level position is obtained from between both the connection lands 110.
Incidentally, when the state of the first contact part 120 of the sliding arm 102 is changed from a state, in which the first contact part 120 is in contact with a given one of the first conductive segments 105, to another state, in which the first contact part 120 is in contact with the adjacent one of the first conductive segments 105, the magnitude of the resistance of the resistive element 106 disposed between an adjoining two of the first conductive segments 105 is increased and decreased stepwise. Thus, a variation in the liquid level is detected as a stepwise change.
Meanwhile, as illustrated in FIG. 13, the first conductive segments 105 and the second conductive segments 107 are placed at the same position nearly in the sliding direction (that is, Y-direction) of the sliding arm 102 at the same intervals T3 in the related apparatus 100 in such a way as to have the same width W3. Therefore, in a section in which the first contact part 120 is in contact with certain one of the first conductive segments 105, the following three states occur. That is, a state in which the second contact part 121 touches only a certain one of the second conductive segments 107, another state in which the second contact part 121 touches this certain second conductive segment 107 and the second conductive segments 107 that are adjacent thereto, and another state in which the second contact part 121 touches only the adjacent second conductive segments 107. Further, the conductor resistance of the second sliding part 104 has different values respectively corresponding to such states. Thus, in the case that the resistance corresponding to the resistance value characteristic of the above electric circuit includes the conductor resistance of the second sliding part 104, variation in the resistance value characteristic occurs. Consequently, variation in the liquid level is not obtained as regular stepwise change.